User guide, package.json: add name and version

[deining]

From the npm docs:

A package.json file must contain "name" and "version" fields.

package.json inside the userguide directory does not have this fields.

As a consequence users may be confronted with poor output like this:

/path/to/docsy/userguide$ npm run-script
Scripts available in undefined via `npm run-script`:
  _build
  ...

This PR corrects this.

[chalin]

Interesting, I had not noticed that behavior of "undefined" being printed when NPM lists the scripts.

I doubt that we need a version since the UG isn't a published package, but I'm ok with this PR. (We might consider removing the version field later.)